Hi

Making a near-future empire builder similar to total war. The player fights for control of cities on the world map. Technology is semi-scifi (you still have factories, tanks, infantry, rockets and nukes, no super-laser robots or star destroyers. But maybe hoovercrafts and powersuits!)

I want a rare resource to be one of the "advanced currency" next to funds. My best idea so far is "rare earth" (as in rare earth elements/metals). Most of these are found in china but i can stretch it to be found in other places as well such as south africa, us/canada, brazil, turkey etc (these places has traces of REE and planned or built extraction).

Any other idea? Something that can be needed for advanced units/aircrafts and/or buildings, but preferably has a real-world distribution and not just found in one place. (I know I can just invent some metal but i'd prefer to not do that). Or do you think the REE idea works fine?

I think your "rare earth" approach could work. Make it a advanced ultra-high density energy source, which can replace petroleum and other energy sources, and has little to no radioactivity, allowing it to be used more easily. Something like a perfect uranium/plutonium. It would power all your near-future tech easily.

It sounds similar to Command and Conquer Tiberium Wars (or others stories, it's not something new, I think). You could take a look at it and see where you can use as inspiration and what you can change to fit your game.

To justify the rare ammount, you could use a big event, such as a asteroid impact, which brings it from space (obs: make it hit the moon or come to pieces before entering earth, so it spreads and not destroy the whole world), or a world-scale earthquake, which brings it from earth core. The event could also justify the wars, as the society would crumble because of it.

Aluminum, titanium, maybe?  Aluminum isn't exactly rare, though.

Rare earths probably do make sense as a resource, given how important they are in electronics these days and for the foreseeable future.

Creating up fictional resources is dicey.  There's only so many elements, and for the most part, we have a pretty good idea of how they combine under normal conditions.  Any kind of Rearden Metal or Tiberium or whatever is starting to veer into fantasy. 

Rare earths aren't actually that rare. So they wouldn't make up for good currency. Also, I don't see how any of these could be suitable for armory or as crafting materials. Only maybe Neodym as a source of magnetic energy generation.

However, I'm pretty sure, artificial materials will grow in importance in the future. We have nano materials and carbon tubes already. I think an enhanced metal won't be too far away (some of which exist even today). In addition to that, scientists are experimenting with artificial bone structures grown in laboratories. Maybe that's something for you

REE are mostly used as catalysts, electronics and batteries right now, so im thinking control systems for weapon systems, computers etc. Tanks would still use conventional metals like steel and aluminum of course.

It's maybe a bit of a stretch but it's the best i got right now. I want something with a physical distribution on the globe, so players can fight for these resources.